The invention relates to a transmission having a traction drive continuously variable unit, and more particularly to such a transmission that is configured to achieve geared neutral operation.
U.S. Pat. No. 5,607,372 discloses a transmission that includes a traction drive continuously variable unit and that is configured to achieve geared neutral operation. This transmission, however, includes a Ravigneaux gearset including a long pinion that contacts two sun gears. Such a gearset may be difficult to manufacture and assemble. Furthermore, this gearset does not scale well for high torque values.
The invention addresses the shortcomings of the prior art by providing a transmission that is configured to achieve geared neutral operation using a traction drive continuously variable unit, but without using a Ravigneaux gearset.
Under the invention, a traction drive transmission includes coaxial input and output shafts and a traction drive continuously variable unit that is connected to the input shaft. The transmission further includes first, second and third gearsets and first and second clutches.
The first gearset is a compound planetary gearset including a first sun gear attached to the continuously variable unit, and a first carrier having a first carrier body attached to the input shaft and the continuously variable unit. The first carrier further has first and second planet pinions rotatably supported by the first carrier body. The first planet pinion meshes with the first sun gear, and the second planet pinion meshes with the first planet pinion. The first gearset further includes a first ring gear that meshes with the second planet pinion. The second gearset has a second carrier attached to the first ring gear, a second ring gear attached to the first carrier body, and a second sun gear. The third gearset has a third sun gear attached to the second sun gear, a third carrier, and a third ring gear. The first clutch is movable between an engaged position, for drivably connecting the second carrier and one of the output shaft and the third carrier, and a disengaged position for disconnecting the second carrier from the one of the output shaft and the third carrier. When the first clutch is in the engaged position, torque supplied by the input shaft is transferred from the first ring gear to the output shaft. The second clutch is movable between an engaged position, for braking one of the third carrier and the third ring gear, and a disengaged position for releasing the one of the third carrier and the third ring gear. When the second clutch is in the engaged position and the first clutch is in the disengaged position, torque supplied by the input shaft is transferred through the third sun gear, then through the other of the third carrier and the third ring gear to the output shaft. Furthermore, the transmission is operative to maintain the output shaft in a stationary position when the input shaft is rotated in a first direction and the first clutch is in the engaged position.